The invention relates generally to bidirectional audio communications and, more particularly, to echo cancellation in such communications.
FIG. 1 illustrates a conventional communication device in which echo cancellation techniques are utilized. The device of FIG. 1 could be, for example, a telephone (fixed or mobile) including a hands-free speaker/microphone arrangement at 14. A signal xfar from a far-end source is reproduced at loudspeaker 11. When the sound emerges from loudspeaker 11, it bounces off of surrounding structures and back into a microphone 13 that also receives a signal xnear from a near-end source. Because of this echo phenomenon, a listener at the far end can actually perceive an echo of the sound produced at the far end.
To eliminate such echos, a filter with adjustable filter taps is conventionally applied as illustrated at 17 and 19 in FIG. 1. The values of the filter taps are controlled by an adaptive algorithm (e.g., a Least Mean Squares algorithm) illustrated at 17 such that the echo canceller filter at 19 resembles as closely as possible the echo path between the loudspeaker 11 and the microphone 13. The estimated echo produced by the echo canceller filter 19 is subtracted at 15 from the signal output from the microphone 13, such that, ideally, only the near-end signal xnear remains as the resulting signal 12.
Conventional techniques of eliminating acoustical echos in communication devices such as illustrated in FIG. 1 have heretofore employed algorithms that operate on the entire frequency range supported by the communication device, for example 300-3400 Hz for a typical conventional telephone.
According to the present invention, improved echo cancellation performance is achieved by dividing the audio signal into subbands, and applying echo cancellation techniques in the subbands. Advantageously, by applying echo cancellation techniques in subbands, the adaptive filter used for echo cancellation can be simplified.